A portion of the material in this patent document is subject to copyright protection under the copyright laws of the United States and of other countries. The owner of the copyright rights has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the United States Patent and Trademark Office publicly available file or records, but otherwise reserves all copyright rights whatsoever. The copyright owner does not hereby waive any of its rights to have this patent document maintained in secrecy, including without limitation its rights pursuant to 37 C.F.R. xc2xa7 1.14.
A portion of the material in this patent document is also subject to protection under the maskwork registration laws of the United States and of other countries. The owner of the maskwork rights has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the United States Patent and Trademark Office publicly available file or records, but otherwise reserves all maskwork rights whatsoever. The maskwork owner does not hereby waive any of its rights to have this patent document maintained in secrecy, including without limitation its rights pursuant to 37 C.F.R. xc2xa7 1.14.
1. Field of the Invention
This invention pertains generally to microwave transceivers used in motion detectors, such as Doppler shifted radar sensors used for detecting a moving target in the security industry, and more particularly to a planar transceiver which employs a chip on board design where all components can be surface mounted.
2. Description of Related Art
Microwave transceivers have been used in many applications, such as traffic surveillance radar systems, point-to-point communications systems, and intrusion detection systems. A microwave transceiver typically generates microwave radiation by means of a waveguide cavity oscillator or a transistor oscillator. The microwave radiation is then radiated into free space by means of a waveguide horn antenna or a microstrip patch antenna. A transistor oscillator using, for example, a field effect or a bipolar transistor, together with a dielectric resonator to stabilize its performance, is normally used for frequencies below approximately 14 GHz. Most commonly a packaged FET or Schottky device is used and soldered into the circuit. Examples of patents describing this type of configuration are U.S. Pat. Nos. 4,630,003, 4,445,097, 5,371,509, and 5,583,523, each of which is incorporated herein by reference.
Various approaches have been taken in the construction of these lower frequency transceivers. For example, GB 2 253 108 A, incorporated herein by reference, shows a multilayer construction where the microwave components and the patch antennas are on separate circuit boards. The microwave circuit board has a component side and a ground plane side, and the antennas are coupled to the microwave circuitry by means of microstrips on the antenna board that are orthogonal to slots in the ground plane that are resonant at the oscillator frequency. This transceiver configuration also uses a dielectric resonator in the oscillator. Another example is U.S. Pat. No. 6,064,276, incorporated herein by reference, which uses a similar approach but has an extra Schottky device for frequency tuning of the oscillator. GB 2 243 495 A, incorporated herein by reference, describes a dielectric resonant oscillator of the type used in the foregoing two patents.
At higher microwave frequencies, such as 24 GHz and above, a beam-lead or Flip-chip Schottky diode is normally used in a microstrip mixer circuit. These diodes, however, are fragile and require a hard plate to support the microstrip substrate. Because of this requirement, high frequency microstrip circuits generally have only one substrate layer as, for example, shown in U.S. Pat. No. 5,832,376 incorporated herein by reference.
Waveguide cavity oscillators are preferred for use at these higher microwave frequencies because the performance of packaged transistors declines at higher frequencies. A Gunn diode (for the oscillator) and Schottky diode) for the mixer are commonly found in waveguide transceivers. Such waveguide transceivers typically include an oscillator, a circulator, a mixer, an antenna, and a waveguide to antenna transition. As shown in U.S. Pat. No. 6,008,750, incorporated herein by reference, a waveguide transceiver has been combined with a microstrip patch antenna to avoid this difficulty. However, because Gunn and Schottky diodes are used in the transceiver, it suffers from the disadvantage of requiring a relatively large amount of manual assembly, and the transceiver is bulky, heavy and costly. Also, the current consumption of a Gunn diode is typically six to eight times higher than that of a low phase noise GaAs MESFET oscillator, thus rendering a waveguide transceiver impractical as a wireless sensor.
Therefore, there is a need for a high frequency microwave transceiver for use as a wireless sensor that is small, lightweight, low cost and which addresses the foregoing and other deficiencies of waveguide transceivers.
The present invention is directed to a novel transceiver design for use in motion sensors, which is of a smaller size, has a lower cost, and has lower current consumption and better performance than conventional transceivers. The invention is suitable for automatic assembly and can be used in wireless security applications.
By way of example, and not of limitation, the foregoing needs are met by a microwave transceiver design where, according to an aspect of the invention, the oscillator comprises a surface mounted FET chip and the mixer comprises a pair of surface mounted Schottky chips, all of which are wire bonded to microstrip circuitry. As a result, a 24 GHz transceiver module according to the invention is of a smaller size, lower cost, lighter weight and more suitable for mass production than conventional transceiver shown in FIG. 4. Beneficially, a microwave transceiver according to a further aspect of the invention is a substantially planar transceiver.
In one embodiment of the invention, the transceiver is a module that includes a soft multilayer printed circuit board made, for example, from a Teflon(copyright)-based material. A patch-type transmit antenna and a patch-type receive antenna are patterned on one side of the multilayer circuit board, while the other circuitry is located on the other side of the multilayer circuit board.
In one embodiment, a microwave circuit board comprising a microstrip oscillator circuit and a microstrip mixer circuit is superimposed over an antenna circuit board comprising a transmit antenna and a receive antenna with a ground plane layer in-between. Each antenna has a respective microstrip that is aligned with an associated microstrip on the microwave circuit board, and the ground plane layer has, for each antenna, a respective slot to provide coupling between the antenna microstrip and the associated microstrip on the microwave circuit board.
According to an aspect of the invention, the oscillator circuit uses a wire bonded surface mounted transistor chip and does not require a dielectric resonator. According to another aspect of the invention, the mixer circuit comprises a balanced mixer that uses a pair of wire bonded surface mounted diode chips. In one embodiment, the transistor chip comprises a field effect transistor. In another embodiment, the mixer diode chip comprises a Schottky diode.
In accordance with another aspect of the invention, the transceiver assembly is disposed within the cavity of a housing in which the transceiver assembly is hermetically sealed.
In one embodiment, the output signal from the local oscillator is coupled through a direct current (DC) block to the input of a power divider. A portion of the local oscillator signal is coupled to the transmit antenna through a first output of the power divider which is coupled to the transmit antenna through a slot in the ground plane. A portion of the local oscillator signal is also coupled to the first input of the mixer through a second output of the power divider. The mixer has a second input for receiving the reflected target signal from the receive antenna through a slot in the ground plane. The mixer combines the local oscillator signal and the target signal to produce a Doppler signal for further signal processing.
In one embodiment, the transceiver assembly comprises an antenna card and a circuit card. The thickness of the microstrip substrate for the antenna card is approximately 20 mil and the thickness of the microstrip substrate for the circuit card is approximately 10 mil. The two cards (substrates) are bonded together by a bonding film and share a common ground (copper layer). The FET chip and the Schottky chip, which are approximately 15 milxc3x9715 mil each, are wire bonded directly to microstrips on the circuit card.
Beneficially, according to an aspect of the invention, a balanced mixer comprising two Schottky chips is used and the transmitting and receiving channels are separated by using two antennas. As result, the performance characteristics such as sensitivity and detection pattern are superior to conventional waveguide transceivers.
A still further aspect of the invention is to surface mount all of the components in the transceiver assembly to render the invention suitable for automatic production and overcome the need for manual assembly.
Beneficially, a transceiver assembly according to the present invention does not require a buffer between the oscillator and the mixer. Furthermore, frequency tuning is accomplished by direct perturbation of a stub on the oscillator circuit.
According to another aspect of the invention, the FET and Schottky chips are directly wire bonded to microstrips on the surface of the multilayer soft substrates. Beneficially, this overcomes the limitation of using transistors at above 20 GHz and difficulties associated with using thin, flexible multilayer substrates at high microwave frequencies.
In accordance with an embodiment of the invention, low cost standard waveguide type Schottky chips are used instead of a surface-mount device such as a lead-beam diode which requires a hard plate for support. Lead-beam diodes are easily broken on flexible transceiver cards.
Advantageously, a transceiver according to the present invention does not require a dielectric resonator to stabilize its oscillation. Dielectric resonators require manual placement which increases the difficulty of production. Optionally, however, a dielectric resonator can be incorporated into the assembly to increase performance at a cost tradeoff.
In accordance with a still further aspect of the invention, the transceiver can operate at different frequencies, such as in the range from 16 GHz to 90 GHz by changing the size of the patch antenna and microstrip circuits and the thickness of the substrate.
In another embodiment of the invention, a modulator is optionally included in the transceiver so that the transceiver can be used for short-range communications.
As can be seen, a microwave transceiver assembly according to the invention is simple, inexpensive, lightweight and compact, thus making it suitable for commercial production and applications. The transceiver employs an all-chip-on-board design which allows for automatic production.
Further aspects of the invention will be brought out in the following portions of the specification, wherein the detailed description is for the purpose of fully disclosing preferred embodiments of the invention without placing limitations thereon.